Fig. 5: RyR2-R420W increased sensitivity to Ca²⁺ is partially reversed by CaM binding.

a Cryo-EM particle population percentage in the samples of PKA-phosphorylated RyR2-R420W + Ca²⁺ in the absence and presence of CaM. b Overlapping models of primed PKA-phosphorylated RyR2-R420W (PDB:8UXF, gray) and primed PKA-phosphorylated RyR2-R420W + Ca²⁺ (PDB:8UXH, magenta). The arrows show that the cytoplasmic shell of the channel shifts downward-outward in the presence of Ca²⁺ inducing a more pronounced primed state. c Overlapping models of primed PKA-phosphorylated RyR2-R420W + Ca²⁺ (PDB:8UXH, magenta) and primed PKA-phosphorylated RyR2-R420W + Ca²⁺ + CaM (PDB:8UXL, cyan). The arrows show that the cytoplasmic shell of the channel shifts upward-inward in the presence of CaM, partially reversing the changes introduced by Ca²⁺. d RMSD normalized projection of RyR2-R420W + Ca²⁺ different states. Values close to 0 or 1 indicate the conformation of the cytoplasmic shell is more similar to the closed WT RyR2, or the open WT RyR2, respectively. e–g Cryo-EM maps of primed PKA-phosphorylated RyR2-R420W (e, gray), primed PKA-phosphorylated RyR2-R420W + Ca²⁺ (f, magenta), and primed PKA-phosphorylated RyR2-R420W + Ca²⁺ + CaM (g, cyan), highlighting the absence of the BSol2 domain (f, dashed circle) and the presence of CaM (g, orange). h, i Aligned models focused on the CaM binding site of primed PKA-phosphorylated RyR2-R420W (gray), primed PKA-phosphorylated RyR2-R420W + Ca²⁺ (magenta), and primed PKA-phosphorylated RyR2-R420W + Ca²⁺ + CaM (cyan). Models were aligned at the TM domain. Conformational changes are indicated with arrows.